Sensors have been used in downhole environments to detect and measure pressure, strain, temperature and other well characteristics that indicate the production capability of the well. These sensors have typically been constructed using piezoelectric and ferroelectric components that are reactive to pressure and temperature characteristics, and have been within the bore of downhole tools to monitor these conditions. Once the measurements are completed, then the downhole tools are retrieved and the data retrieved for analysis of the downhole conditions. This process of retrieving data is time consuming and also requires stopping well production. This time translates into lost profits and increased operational costs of the well.
Pressure, temperature, flow, and water cut are fundamental measurements for the management of producing wells. In deepwater operations and high producing horizontal/multilateral wells, these measurements take on an increased significance. Oil producers have been incurring costs to monitor wells in these complex oil well environments using antiquated technology.
For example, sensors have been developed and deployed to remain downhole to monitor conditions in producing wells. These sensors, however, are single-point electronic sensors that are very expensive and have a mean-time-to-failure much lower than optimal. As a result, and despite the full complement of sensors, the majority of a well structure after a short time is monitored by less than the complement of sensors.
As an advance in sensor technology, Bragg grating technology has emerged as an alternative to single-point sensors due to its fiber optic sensing transducer capability. Due to their narrowband wavelength reflection, they can be multiplexed in a fiber optic network. Nevertheless, such sensors can be susceptible to the hostile downhole environments, and, as a consequence, fail to operate for a time far shorter than the producing life of a well. Thus, a need exists for simplified optical sensors that have a robust housing to withstand the large magnitude forces downhole while still sufficiently yielding to reliably sense the environment conditions.